This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2001-365049 and 2001-327868 filed in JAPAN on Nov. 29, 2001 and Oct. 25, 2001, respectively, which is herein incorporated by reference.
The present invention relates to a method and apparatus for detecting decrease in tire air-pressure and a program for judging decompression of a tire. More particularly, it relates to a method and apparatus for detecting decrease in tire air-pressure and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of two wheel tires on the same side of a four-wheeled vehicle or simultaneous decompression of both front tires or both rear tires while it is further possible to detect decompression of a single wheel tire.
An apparatus for detecting decrease in tire air-pressure (DWS) in which decompression of a tire is detected on the basis of rotational (wheel speed) information of four wheel tires attached to a vehicle is conventionally known. The apparatus employs a theory that a rotational velocity or a rotational angular velocity of a compressed tire is increased when compared to remaining normal tires owing to a decrease in outer diameter (dynamic load radius of the tire) from that of a tire of normal internal pressure. In a method for detecting decrease in internal pressure on the basis of a relative difference in rotational angular velocities of tires (reference should be made to Japanese Unexamined Patent Publication No. 305011/1988),
DEL={(F1+F4)/2xe2x88x92(F2+F3)/2}/{(F1+F2+F3+F4)/4}xc3x97100(%) 
is employed as a judged value DEL. Here, F1 to F4 denote rotational angular velocities of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
However, since decompression is judged on the basis of a difference in sums of rotational angular velocities of the four wheels which are respectively located diagonally with respect to each other, it is impossible to detect simultaneous decompression of all left-sided wheels or all right-sided wheels (two wheel tires on the same side). It is further impossible to detect simultaneous decompression of both front wheels or both rear wheels. Therefore, there exists a danger that fuel consumption is worsened through increase in rolling resistance of the tire and that a burst might be caused upon continuing running without being aware of decompression.
In view of the above facts, it is an object of the present invention to provide a method and apparatus for detecting decrease in tire air-pressure and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of two wheel tires on the same side of a four-wheeled vehicle or simultaneous decompression of both front tires or both rear tires while it is further possible to detect decompression of a single wheel tire.
In accordance with a first aspect of the present invention, there is provided a method for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The method includes the steps of: detecting rotational information of the respective tires; storing the rotational information of the respective tires; comparing rotational information of all left-sided wheels and rotational information of all right-sided wheels of the vehicle when the vehicle is performing straight-ahead running; and judging decompression on the basis of a relationship between a value obtained through comparison of the left-sided and right-sided rotational information and a specified threshold.
In accordance with a second aspect of the present invention, there is provided an apparatus for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The apparatus includes: rotational information detecting means for detecting rotational information of the respective tires; a rotational information storing means for storing the rotational information of the respective tires; a comparing means for comparing rotational information of all left-sided wheels and rotational information of all right-sided wheels of the vehicle when the vehicle is performing straight-ahead running; and a decompression judging means for judging decompression on the basis of a relationship between a value obtained through comparison of the left-sided and right-sided rotational information and a specified threshold.
In accordance with a third aspect of the present invention, there is provided a program for judging decompression of a tire, in which for judging decrease in tire air-pressure of a tire, a computer is made to function as a rotational information storing means for storing the rotational information of the respective tires; a comparing means for comparing rotational information of all left-sided wheels and rotational information of all right-sided wheels of the vehicle when the vehicle is performing straight-ahead running; and a decompression judging means for judging decompression on the basis of a relationship between a value obtained through comparison of the left-sided and right-sided rotational information and a specified threshold.
In accordance with a fourth aspect of the present invention, there is provided a method for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The method includes the steps of: detecting rotational information of the respective tires; storing the rotational information of the respective tires; comparing rotational information of both front wheels and rotational information of both rear wheels of the vehicle when the vehicle is performing straight-ahead running and neither driving nor braking force is acting on the tires; and judging simultaneous decompression of both front wheels or simultaneous decompression of both rear wheels on the basis of a relationship between a value obtained through comparison of the rotational information of both front wheels and the rotational information of both rear wheels and a specified threshold.
In accordance with a fifth aspect of the present invention, there is provided an apparatus for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The apparatus includes: rotational information detecting means for detecting rotational information of the respective tires; a rotational information storing means for storing the rotational information of the respective tires; a comparing means for comparing rotational information of both front wheels and rotational information of both rear wheels of the vehicle when the vehicle is performing straight-ahead running and neither driving nor braking force is acting on the tires; and a decompression judging means for judging simultaneous decompression of both front wheels or simultaneous decompression of both rear wheels on the basis of a relationship between a value obtained through comparison of the rotational information of both front wheels and the rotational information of both rear wheels and a specified threshold.
In accordance with a six aspect of the present invention, there is provided a program for judging decompression of a tire, in which for judging decrease in tire air-pressure of a tire, a computer is made to function as a rotational information storing means for storing the rotational information of the respective tires; a comparing means for comparing rotational information of both front wheels and rotational information of both rear wheels of the vehicle when the vehicle is performing straight-ahead running and neither driving nor braking force is acting on the tires; and a decompression judging means for judging simultaneous decompression of both front wheels or simultaneous decompression of both rear wheels on the basis of a relationship between a value obtained through comparison of the rotational information of both front wheels and the rotational information of both rear wheels and a specified threshold.